This invention relates to improvements on raw ceramic powder material adapted to provide a sintered ceramic product of high mechanical strength and more particularly to improvements on raw ceramic powder material mainly consisting of silicon nitride.
Worldwide studies have been made of sintered silicon nitride which displays prominent mechanical strength at high temperature. Known processes developed to this end include, for example, that which hot-presses silicon nitride powder mixed with magnesia, and that which similarly hot-presses silicon nitride powder mixed with yttria. These processes are found to provide a dense sintered product of silicon nitride. However, a more dense construction does not offer excellent mechanical strength at high temperature. The reason is that a simply densified sintered product contains glassy material, which gives rise to a decline in the high temperature mechanical strength of the product.
The present inventors have studied the optimum composition of raw ceramic powder material to decrease the content of glassy component, and accomplished the present invention.
It is accordingly an object of this invention to provide raw ceramic powder material adapted to manufacture a sintered product having excellent mechanical strength at high temperature.
Another object of the invention is to provide such raw ceramic powder material as enables the content of glassy material in a sintered product to be decreased.
Still another object of the invention is to provide a method for efficiently preparing the above-mentioned raw ceramic powder material.
The other objects will be apparent from the following description.